Magnetic structure having a fixed and variable air gap



1965 CHARPENTIER 3,204,155

MAGNET STRUCTURE HAVING A FIXED AND VARIABLE AIR GAP Filed July 31. 19614 Sheets-Sheet l Fig.5 L

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Aug. 31, 1965 R. CHARPENTIER MAGNETIC STRUCTURE HAVING A FIXED ANDVARIABLE AIR GAP 4 Sheets-Sheet 2 Filed July 31. 1961 Allg- 1965 R.CHARPENTIE 3,204,155

MAGNETIC S HAVI TRUCTURE N FIXED AND VARIABLE AIR GAP Filed July 31.1961 4 Sheets-Sheet s IE6 6 4" R\\\ 1 4 z- 2 2/\ 11 A 4 m 6 4 Fig [5F79. 76

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MAGNETIC STRUCTURE HAVING A FIXED AND VARIABLE AIR GAP Filed July 51,1961 4 Sheets-Sheet 4 E Q Q g-pa suag H p ay uo/ p2l au5owaa' 003 005005 .nDLL /r Q m Lu .A in 0a 1 Q: Q B I: a m I: G Inauc/z'oo -B-ki/ogauss United States Patent 3,204,155 MAGNETIC STRUCTURE HAVING AFIXED AND VARIAllLE AIR GAP Roger Charpentier, 27 bis Ave. des Lilas,Pau, Basses-Pyrenees, France Filed July 31, 1961, Ser. No. 128,098Claims priority, application France, July 29, 1960, 834,372, Patent1,272,074; Dec. 22, 1960, 847,671 Claims. (CL 317-201) For a magnet tobe economically useful it is necessary for it to work in a zone of thedemagnetization curve in which the product of its induction B and thedemagnetizing field H has its maximum value or is close to this value;this result is obtained by giving predetermined dimensionalcharacteristics to the magnet and to the gap existing between the polesor the pole pieces.

In practice, in particular for magnetic catches, one generally uses themagnet, not by itself, but in combination with two pole pieces such asis seen in FIGURE 1 in which the references 1 and 2 indicaterespectively the magnet and the pole pieces. To obtain the maximum valuefor the product BH, the length L of the magnet is made relatively greatwith respect to the cross section S, particularly for Ticonal magnets ormagnets having a similar demagnetization curve. Ticonal is a magnet madeof an iron base alloy containing, in addition, cobalt, nickel andaluminum. The content of cobalt is between 16 and 30%; that of nickel isbetween 12 and 20%; and that of aluminum is between 6 and 11%.

. There exist in practice several varieties of Ticonal. That which ismost common has the following composition:

Percent Cobalt 24 Nickel 14 Aluminum 8 Copper 3 The remainder beingiron.

Variations contain, in addition to the above proportions of nickel,cobalt, aluminum and copper, a titanium content of between 0.5 and 1.5%.

The above compositions of Ticonal, together with their characteristics,are listed and identified as Ticonal in a published table which liststhe different varieties (and their characteristics) of permanent magnetsthat were on the market in 1957. The table was published in issue No. 4of the Revue de Cobalt (pages 36-39) published in September 1959, and isa reproduction of a table which appeared in the February 1957 issue ofthe Electrical Energy Revue (Electrical Energie). Just below the middleof the table on page 38 there appear several listings of Ticonal withthe compositions indicated above, together with the residual magnetismBr in gauss, the maximum value of the product (BH) expressed in 10gauss-oersteds, the magnetomotive force H in oersteds, and the density.

The applicant has sought to reduce the length of the magnet and hasrealized that it was possible, in spite of this reduction, to make themagnet function in the best conditions it two non-magnetic gaps areprovided, one fixed, the other variable according to the distance of thearmature cooperating with the pole pieces, and by giving the magnet andthe pole pieces dimensions and shapes according to precise conditions,these dimensions and shapes permitting the obtaining of a product ofpermanence which is favorable to a good distribution of the flux,whatever the distance of the armature from the pole pieces.

Consequently the present invention has for an object a practicalarrangement, particularly for magnetic catches, comprising a magnet andtwo pole pieces arranged in a manner to give a double gap of which onegap is fixed and the other variable. For a Ticonal type magnet or onehaving a similar curve and of which the dimensions have the followingproportions that is to say working at an unfavorable point on thedemagnetisation curve, its point on the curve will be caused to ascend,thus augmenting the product BH, if one adopts, for the pole pieces, theshapes and proportions which give a fixed gap of which the proportionswill be between:

and a surface s" in this fixed gap:

It is also preferred that for s If these conditions are observed,experience shows that the total of the fixed permanences, variable andleakage, is such, in open circuit, that the magnet operates in optimumconditions, that is to say the value of the product B H approaches itsmaximum.

When the armature is at a considerable distance from the pole pieces,the total flux of the magnet is distributed between the circuit of thefixed air gap and leakages-the magnet operating in the neighborhood ofthe maximum of the product BH-the dimensions of the fixed gap are suchthat the length and the cross-section of this gap may be great, similarto the cross-section of the surrounding iron. In this way, one part ofthe iron is close to saturation, on the other hand, the leakage awayfrom the large surfaces are great.

When the armature is relatively close to the pole pieces, a new field isoffered for the passage of flux, and the total permanence of thecircuits increased; the magnetomotive force of the magnet diminishes(the magnet moves up its curve). The leakage diminishes proportionallyto the reduction of the magnetomotive force of the magnet and just asthe leakage was important when the armature was distant, the reductionis equally important.

On the other hand, thanks to the big cross-section of iron of thecircuit of the fixed gap, the flux which passes through this circuitdiminishes equally and proportionally to the reduction of themagnetomotive force of the magnet, while if the iron section were to besmall, the flux would diminish less quickly than the magnetomotive force(with a small cross section of iron, when the armature is remote, themagnetomotive force becomes such as to force the flux to pass throughthe iron and this represents a waste of the flux).

The choice of the dimensions of the fixed air gap thus creates twoconditions: a rapid reduction of the leakage, a slow reduction of theflux passing through the fixed air gap, which ensure that the part ofthe flux which passes through the armature is a maximum, thus theattraction is a maximum even when the armature has not yet contacted thepole pieces.

There is described hereafter, by way of example only, variousconstructions of magnet according to the invention, reference being madeto the accompanying drawings in which:

FIGURE 2 is a view in longitudinal section of a first construction ofmagnet according to the invention;

FIGURE 3 is a view similar to FIGURE 2 of a second construction;

FIGURE 4 is a section along the line IVIV of FIGURE 3;

FIGURE 5 is a plan view of a third construction;

FIGURE 6 is a View in sectional elevation of FIG- URE 5;

FIGURE 7 is a sectional view of a fourth construction;

FIGURE 8 is a plan view of FIGURE 7;

FIGURES 9 and 11 are views similar to FIGURE 7 of two modifications;

FIGURES and 12 are plan views corresponding respectively to FIGURES 9and 11;

FIGURE 13 is a sectional view of another construction;

FIGURE 14 is a plan view of the construction of FIG- URE 13;

FIGURE 15 is a sectional view of a further construction;

FIGURE 16 is a sectional view along the line XVIXVI of FIGURE 15;

FIGURE 17 is a section of another construction;

FIGURE 18 is a plan view of the construction shown in FIGURE 17;

FIGURE 19 is a view in elevation of another construction;

FIGURE 20 is a section along the line XXXX of FIGURE 19;

FIGURE 21 is a modification of the construction shown in FIGURE 19;

FIGURE 22 is a view along the line XXII-XXII of FIGURE 21; and

FIGURE 23 is a graph showing the demagnetization curves of severalmaterials which may be used for the construction of the magnet of thepresent invention.

FIGURE 1 shows the known construction in which references 1 and 2indicate respectively the magnet and the pole pieces. To obtain themaximum value for the product BH, the length L of the magnet 1 must berelatively large by comparison with the cross-section S.

In FIGURE 2, each of the pole pieces has a contact surface s for anarmature 3 and has in its rear part a transverse portion 2a; these twoportions 2a are so located that there exists at the rear of the magnet afixed nonmagnetic gap 4 of length 0, the cross-section of the portions2a of the pole pieces constituting this gap having a value s".

The magnet 1 being in Ticonal or in a material having a demagnetizationcurve analogous to that of Ticonal, its length being between /S and/S/2, one chooses according to the present invention a length e for thegap between L/ 15 and L/3 and preferably equal to L/8, at the same timethe surface s", at this gap is chosen to be between 58/12 and 38.

The contact surface s of each of the pole pieces with the armature is,preferably, between S/ 3 and S.

In the construction of FIGURES 3 and 4 there is also a doublenon-magnetic gap, but the pole pieces 2 are planar and the fixed gap,which in this case is double, is obtained by locating a piece of softiron 5 behind the magnet 1 at a distance e/2 from each of the polepieces, this soft iron piece being held in place, for example, bymembers of non-magnetic material in the spaces between the soft ironpiece and the pole pieces and between the soft iron piece and themagnet. In a modification, the soft iron member is arranged to be incontact with one of the pole pieces and at a distance e from the other.

In the arrangement of FIGURES 5 and 6, the magnet '1 and the pole pieces2 are arranged in the form of a cylinder. The external shape of the twopole pieces 2 is substantially semi-cylindrical, their axes beingperpendicular to the magnetic axis of the magnet 1. Their edges areseparated one from the other to form two fixed gaps of length e, whichare located on opposite sides of the magnet. The armature 3 is movablealong the axis of the cylinder parallel to the longitudinal direction ofthe fixed gaps.

As may be seen from these figures, each of said pole pieces is so shapedthat magnetic flux traveling in a circular manner in a directionperpendicular to the cylindrical axis of the magnet assembly finds itspath substantially narrowed at two points on each pole piece (at eachedge of the area of contact between the magnet and the pole piece) insuch a way that the pole pieces become easily saturated in thevicinities of these constrictions. This saturation tends to urge a largeproportion of the flux to act on armature 3 as it approaches the polepieces and thus tends to substantially increase the magnetic attractionexerted on the former.

The construction of FIGURES 7 and 8 is generally similar to that ofFIGURES 3 and 4 but the pole pieces 2 have a substantially cylindricalexternal shape so as to form part of a cylinder. Their inner face isplanar and abuts the magnet 11, the latter being surmounted by a softiron member 5 located at a distance 6/ 2 from each of the pole pieces.

The construction of FIGURES 9 and 10 is different from that of FIGURES 7and 8 in that the fixed gap is obtained by means of a soft iron piece 6located at a distance e/ 2 from the end of the pole pieces 2 opposite tothe movable armature.

The arrangement of FIGURES 11 and 12 is a combination of the twopreceding constructions. The fixed gap is provided by a soft iron piece7 providing a circular part surmounting the pole pieces 2 and asubstantially parallelepiped portion which is arranged between the polepieces above the magnet 1.

In the construction of FIGURES 13 and 14, the fixed gap is obtained bymeans of a soft iron sleeve 8 the interior radius of which is greaterthan the external radius of the pole pieces 2 by an amount equal to e/2.

The construction of FIGURES 15 and 16 is a modification of that ofFIGURES 9 and 10 in which the pole pieces 2 are planar.

In the construction of FIGURES 17 and 18, the magnet 1 is surrounded bya soft iron piece 9 of U-section and is located at a distance e/2 fromeach of the pole pieces 2.

In the construction of FIGURES 19 and 20, the fixed gap is obtained bymeans of a soft iron sleeve 10 which surrounds the magnet I and whoseaxis is coaxial with the magnetic axis of the magnet 1, the latter beingof circular cross-section in this construction. The length of this softiron sleeve is less than the distance between the pole pieces, which areplanar, by an amount equal to e. Each edge of this soft iron sleeve isat a distance e/ 2 from the respective pole piece.

In the modifications of FIGURES 21 and 22, one of the edges of the softiron sleeve 10 is in contact with one of the pole pieces and is locatedat a distance e from the other pole piece.

In the various constructions, the gap or gaps can be filled by anon-magnetic material and the dimensions of the pole pieces and of themagnet are determined in accordance with the above indicated conditions.

FIG. 23 is a graph showing the demagnetization curves of severalmaterials, from which the magnet 1 of the various embodiments describedabove may be made. These materials have been selected only by way ofexample and it should be understood that other varieties having similarcurves may be used. These curves are plotted in terms of the induction(B) in kilogauss vs. the demagnetization field (H) in oersteds and showthat the mater als represented, i.e., Ticonal G D (Ugimax) and Ticonal600, 700, 750 and 800, all of which are the designations under whichthese materials are sold, have in common that the flux density (B) ishigh for low values of the demagnetization field and decreases rapidlywith increases in the field after this field increases beyond a certainvalue.

It will be understood that the invention is not limited to theconstructions described and illustrated, but to the contrary covers allmodifications.

I claim:

1. A magnet composed of an aluminum-nickel-cobaltcopper-iron basecomposition, and having a length L between /S/ 2 and /S, the magnetbeing combined with pole pieces arranged to provide a doublenon-magnetic gap of which one is fixed and theother variable, thedimensions of the fixed gap satisfying the following conditions:

S is the area of contact of the magnet with the pole pieces,

L is the length of the magnet between the surfaces of con tact with thepole pieces,

e is the length of the fixed gap,

s the surface area of each of those parts of the pole pieces which formthe fixed air gap.

2. A magnet according to claim 1, wherein the fixed gap furthersatisfies the following condition where S has the above significationand s represents the area of contact of each of the pole pieces with thearmature. 3. A magnet according to claim 1, wherein the pole piecesprovide two fixed non-magnetic gaps located on opposite sides of themagnet.

4. A magnet according to claim 1 wherein the fixed gap is formed by apiece of soft iron located behind the magnet between the pole pieces,the latter having planar or substantially planar inner faces.

5. A magnet according to claim 1 wherein the magnet and the pole piecesform a cylinder.

6. A magnet according to claim 1 wherein the direction of the fixed gapis perpendicular to the direction of movement of the armature.

7. A magnet according to claim 1 wherein the direction of the fixed gapis parallel to the direction of movement of the armature.

8. A magnet according to claim 1, wherein the fixed gap is formed by asoft iron member located above the end of the pole pieces opposite tothe armature.

9. A structure comprising a magnet, the poles of which are situatedlaterally, and two pole pieces arranged on the poles of the magnet andprotruding beyond the end faces of the magnet, each of the longitudinaledges of one of the pole pieces being adjacent to one of thelongitudinal edges of the other pole piece, so as to form two air gapsarranged substantially symmetrically with respect to the longitudinalaxis of the magnet so that the longitudinal axes of said air gaps areperpendicular to those surfaces of said pole pieces which contact anarmature.

10. A structure as recited in claim 9 wherein said pole pieces presentat least one constriction to the flux flowing perpendicularly to saidlongitudinal edges of said pole pieces.

References Cited by the Examiner UNITED STATES PATENTS 2,812,203 11/57Scholten 317159 3,095,525 6/63 Hansen 317201 BERNARD A. GILHEANY,Primary Examiner.

SAMUEL BERNSTEIN, JOHN F. BURNS, LARAMIE E. ASKINS, Examiners.

1. A MAGNET COMPOSED OF AN ALUMINUM-NICKEL-COBALTCOPPER-IRON BASECOMPOSITION, AND HAVING A LENGTH L BETWEEN $S/2 AND $S, THE MAGNET BEINGCOMBINED WITH POLE PIECES ARRANGED TO PROVIDE A DOUBLE NON-MAGNETIC GAPOF WHICH ONE IS FIXED AND THE OTHER VARIABLE, THE DIMENSIONS OF THEFIXED GAP SATISFYING THE FOLLOWING CONDITIONS: